The androgen receptor, RET (REarranged during Transfection), DCC (Deleted in Colorectal Cancer), and UNC5H1-3 (Unc-5 homologues 1-3) are members of a growing list of dependence receptors. Such receptors, by inducing apoptosis when expressed in a setting in which their ligands are unavailable, create a cellular state of dependence on their ligands for survival. Of interest is that all of these receptors are involved in cancer progression, central nervous system-associated diseases and/or development of the nervous system. As an example, DCC encodes a potential tumor suppressor but at the same time is a key receptor in mediating axon guidance induced by the cue netrin-1. By focusing our study on DCC, we propose to define (i) the molecular mechanisms allowing the induction of apoptosis in the absence of ligand, and those mechanisms that block apoptosis in the presence of ligand, (ii) the in vivo function of these dependence receptors, and specifically in the case of DCC, the role of DCC-induced apoptosis inaxon guidance during nervous system development. We will define the molecular mechanisms startingfrom our initial observation that DCC serves as the core for a complex allowing caspase activation.Experiments will include two-hybrid studies using the pro-apoptotic region of DCC (amino acids 1121-1290) as bait, purification and characterization of the proteins contained in the 800,000 Dalton complexformed with DCC, and determination of the presence and the role of DCC multimerization. The in vivo relevance of the pro-apoptotic effect of DCC will be studied by monitoring DCC cleavage by caspasesduring development of the nervous system and by creating knock-in mice expressing a mutated form ofDCC that is unable to induce apoptosis.